1. Technical Field
The present invention relates to semiconductor devices and, more particularly, to stress memorization in replacement metal gate transistors.
2. Description of the Related Art
Conventional transistors are formed with polysilicon gate material. Polysilicon has been used due to its thermal resistive properties. Polysilicon's robustness during high temperature processing allows it to be annealed at high temperatures, along with source and drain regions. Furthermore, its ability to block the ion implantation into a channel region is advantageous. However, polysilicon gates have certain disadvantages. For example, polysilicon gate electrodes are formed from semiconductor materials that suffer from higher resistances than most metals. Therefore, polysilicon gate electrodes operate at lower speeds than gates made of metallic materials.
To address this problem, replacement metal gate (RMG) transistors are used. Metal gates have much lower resistances, allowing for higher gate currents and faster switching.